Effects of l carnitine supplementation on weight loss and body composition: A systematic review and meta analysis of 37 randomized controlled clinical trials with dose response analysis ScienceDirect Do You Know How Long It Takes L carnitine To Start Working? Plix Early research into L carnitine was often cited as underwhelming, showing negligible changes in muscle carnitine content and fat loss outcomes. However, these findings may have been limited by a short study window Frontiers Association between fatigue, peripheral serotonin, and L carnitine in hypothyroidism and in chronic fatigue syndrome